Synthesis, characterization and striking photoluminescence variation of a series of copper(I) complexes containing oxadiazole ligand

A series of novel photoluminescent copper(I) complexes with the formula [Cu(P-P)(L)]BF4, where P-P = triphenylphosphine (PPh3) (1, 2), bis[2-(diphenylphosphino)phenyl]-ether (POP) (3, 4), L = 2-phenyl-5-(pyridin-2-yl)-1,3,4-oxadiazole (L1) (1, 3), 2-(pyridin-2-yl)-5-p-tolyl-1,3,4-oxadiazole (L2) (2, 4), have been successfully synthesized and characterized by elemental analysis, 1H NMR and IR spectra. X-ray crystal structure analysis has been carried out on 1, 2 and 3. Photoluminescence properties of 2 are unique in three respects: (1) an obvious emission blue shift, (2) a high quantum yield (0.94) comparing with the other three complexes (<0.03), and (3) a longer excited state lifetime than those of the others. Systematic analysis suggests that its drastic enhancement in photoluminescence performances is triggered by the extraordinary rigid pseudo sandwich structure constructed from strong intra- and inter-molecular π–π stacking interactions in its crystal structure.